Why do you need dot-slash before executable or script name to run it in bash

Question

When running scripts in bash  I have to write    in the beginning       manage py syncdb   If I don t  I get an error message     manage py syncdb -bash  manage py  command not found   What is the reason for this  I thought   is an alias for current folder  and therefore these two calls should be equivalent   I also don t understand why I don t need    when running applications  such as   user  home user  cd  usr bin user  usr bin  git    which runs without

User · Answer

When the script is not in the Path its required to do so  For more  info read http   www tldp org LDP Bash-Beginners-Guide html sect 02 01 html

User · Answer

On  nix  unlike Windows  the current directory is usually not in your  PATH variable  So the current directory is not searched when executing commands  You don t need    for running applications because these applications are in your  PATH  most likely they are in  bin or  usr bin

User · Answer

All has great answer on the question  and yes this is only applicable when running it on the current directory not unless you include the absolute path  See my samples below   Also  the  dot-slash  made sense to me when I ve the command on the child folder tmp2   tmp tmp2  and it uses  double dot-slash      SAMPLE    fifiip-172-31-17-12 tmp     StackO sh  Hello Stack Overflow   fifi ip-172-31-17-12 tmp    tmp StackO sh  Hello Stack Overflow   fifi ip-172-31-17-12 tmp   mkdir tmp2   fifi ip-172-31-17-12 tmp   cd tmp2    fifi ip-172-31-17-12 tmp2      StackO sh  Hello Stack Overflow

User · Answer

Your script  when in your home directory will not be found when the shell looks at the  PATH environment variable to find your script   The    says  look in the current directory for my script rather than looking at all the directories specified in  PATH

User · Answer

This question already has some awesome answers  but I wanted to add that  if your executable is on the PATH  and you get very different outputs when you run     executable   to the ones you get if you run   executable    let s say you run into error messages with the one and not the other   then the problem could be that you have two different versions of the executable on your machine  one on the path  and the other not   Check this by running  which  executable  and   whereis executable   It fixed my issues   I had three versions of the executable  only one of which was compiled correctly for the environment

User · Answer

Because on Unix  usually  the current directory is not in  PATH   When you type a command the shell looks up a list of directories  as specified by the PATH variable  The current directory is not in that list   The reason for not having the current directory on that list is security   Let s say you re root and go into another user s directory and type sl instead of ls  If the current directory is in PATH  the shell will try to execute the sl program in that directory  since there is no other sl program   That sl program might be malicious   It works with    because POSIX specifies that a command name that contain a   will be used as a filename directly  suppressing a search in  PATH  You could have used full path for the exact same effect  but    is shorter and easier to write   EDIT  That sl part was just an example  The directories in PATH are searched sequentially and when a match is made that program is executed  So  depending on how PATH looks  typing a normal command may or may not be enough to run the program in the current directory

User · Answer

When bash interprets the command line  it looks for commands in locations described in the environment variable  PATH   To see it type    echo  PATH   You will have some paths separated by colons  As you will see the current path   is usually not in  PATH  So Bash cannot find your command if it is in the current directory  You can change it by having   PATH  PATH     This line adds the current directory in  PATH so you can do   manage py syncdb   It is not recommended as it has security issue  plus you can have weird behaviours  as   varies upon the directory you are in     Avoid   PATH    PATH   As you can    mask    some standard command and open the door to security breach         Just my two cents

User · Answer

When you include the     you are essentially giving the  full path  to the executable bash script  so your shell does not need to check your PATH variable   Without the     your shell will look in your PATH variable  which you can see by running echo  PATH to see if the command you typed lives in any of the folders on your PATH   If it doesn t  as is the case with manage py  it says it can t find the file   It is considered bad practice to include the current directory on your PATH  which is explained reasonably well here  http   www faqs org faqs unix-faq faq part2 section-13 html

User · Answer

Rationale for the   POSIX PATH rule  The rule was mentioned at  Why do you need     dot-slash  before executable or script name to run it in bash  but I would like to explain why I think that is a good design in more detail   First  an explicit full version of the rule is    if the path contains    e g    someprog   bin someprog    bin someprog   CWD is used and PATH isn t if the path does not contain    e g  someprog   PATH is used and CWD isn t   Now  suppose that running   someprog   would search    relative to CWD first relative to PATH after   Then  if you wanted to run  bin someprog from your distro  and you did   someprog   it would sometimes work  but others it would fail  because you might be in a directory that contains another unrelated someprog program   Therefore  you would soon learn that this is not reliable  and you would end up always using absolute paths when you want to use PATH  therefore defeating the purpose of PATH   This is also why having relative paths in your PATH is a really bad idea  I m looking at you  node modules bin   Conversely  suppose that running     someprog   Would search    relative to PATH first relative to CWD after   Then  if you just downloaded a script someprog from a git repository and wanted to run it from CWD  you would never be sure that this is the actual program that would run  because maybe your distro has a    bin someprog   which is in you PATH from some package you installed after drinking too much after Christmas last year   Therefore  once again  you would be forced to always run local scripts relative to CWD with full paths to know what you are running      pwd  someprog    which would be extremely annoying as well   Another rule that you might be tempted to come up with would be      relative paths use only PATH  absolute paths only CWD   but once again this forces users to always use absolute paths for non-PATH scripts with    pwd  someprog    The   path search rule offers a simple to remember solution to the about problem    slash  don t use PATH no slash  only use PATH   which makes it super easy to always know what you are running  by relying on the fact that files in the current directory can be expressed either as   somefile or somefile  and so it gives special meaning to one of them   Sometimes  is slightly annoying that you cannot search for some prog relative to PATH  but I don t see a saner solution to this

[bash] Why do you need ./ (dot-slash) before executable or script name to run it in bash?

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